Heterogeneous distribution of metal nanocrystals in glazes of

Applied Surface Science 185 (2002) 206–216
Heterogeneous distribution of metal nanocrystals
in glazes of historical pottery
I. Borgiaa, B. Brunettia,*, I. Mariania, A. Sgamellottia, F. Cariatib,
P. Fermob, M. Mellinic, C. Vitic, G. Padelettid
a
INSTM and Dipartimento di Chimica, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
b
INSTM and Dipartimento CIMA, Università di Milano, Via Venezian 21, 20133 Milan, Italy
c
Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, 53100 Siena, Italy
d
CNR-ICMAT, Via Salaria Km. 29,300, CP 10, 00016 Monterotondo Stazione, Rome, Italy
Received 28 July 2001; accepted 21 September 2001
Abstract
It has been recently shown that lustre decoration of medieval and renaissance pottery consists of silver and copper
nanocrystals, dispersed within the glassy matrix of the ceramic glaze. Lustre surfaces show peculiar optical effects such as
metallic reflection and iridescence. In many cases, lustre appears overlapped to colored drawings. Here we report the findings
of a study on glazes, pigments and lustre of several shards belonging to Deruta and Gubbio pottery of XVI century. The
components of glazes and pigments have been identified. Lustre is confirmed to be characterised by silver and copper metal
nanocrystals inhomogeneously dispersed in the glassy matrix of the glaze. In the case of lustre overlapped to colored
decorations, we found two contradictory cases. The first consists of a lustre surface successfully applied over a blue smalt
geometrical drawing. The second consists of a lustre surface, unsuccessfully applied over a yellow lead-antimonate pigment.
The yellow pigment hinders the formation of lustre and removes crystals of tin dioxide, normally present in the glaze as
opacifier. # 2002 Elsevier Science B.V. All rights reserved.
PACS: 61.46.þw clusters; Nanoparticles; Nanocrystalline materials
Keywords: Nanoparticles; Glass–metal composites; Historical pottery; Lustre
1. Introduction
Lustre was one of the most important decorative
techniques of medieval and renaissance pottery of the
Mediterranean basin. It consisted of a metal deposition
on a tin-opacified lead glaze which produced brilliant
*
Corresponding author. Tel.: þ39-75-5855509;
fax: þ39-75-5855606.
E-mail address: [email protected] (B. Brunetti).
reflections of different colors and iridescence [1].
Historically, lustre was first used during IX century
A.D. to decorate pottery of Mesopotamia. The technique, later used in Egypt during the Fatymid period
(X century), spread all along the Mediterranean basin
together with the diffusion of Islamic culture (X–XIV
century). Lustre decorations reached their maximum
development first in Spain, from XIV to XVI century,
with the productions of Paterna and Manises, and later
in Italy, from XV to XVI century, with the manufactures of Deruta and Gubbio, where lustre was used to
0169-4332/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 9 - 4 3 3 2 ( 0 1 ) 0 0 6 5 9 - 6
I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
decorate the finest polychrome pottery of the Italian
renaissance [1–4].
Lustre was prepared through a procedure consisting
of a ‘‘third firing’’ deposition of a thin film of copper
and silver crystals onto the surface of a previously
glazed and decorated pottery. The deposition was
applied with the brushing over of a mixture of silver,
copper, and iron salts or oxides, together with vinegar
and additional substances. The temperature was then
raised to approximately 600 8C and a reducing atmosphere was produced. In these conditions: (a) glaze
softened; (b) silver and copper compounds were
reduced to metals; (c) metal was deposited within
the outer layers of the glaze, which remained trapped
there [5,6].
Surprisingly, recent work demonstrated that lustre
consists of a heterogeneous metal–glass composite
film, some hundreds of nanometres thick, analogous
to that present in the modern metal–glass nanostructured composites, obtained by ion implantation, ionexchange or sol–gel deposition on pure silica matrices,
followed by annealing under reducing atmosphere
[7–9]. In the lustre, separate silver and copper pseudospherical nanocrystals appear to be dispersed within
the outer layers of the glaze [7]. Although overall
heterogeneous, the nanocrystal distribution can be
locally homogeneous, being characterised, in specific
regions, by constant dimensions and constant density
of nanocrystals. However, crossing the lustre layer
towards the ceramic support, the nanocrystal dimensions decrease from tens of nanometres to a few
nanometres [7].
The optical properties of lustre are connected with
the specific nanostructures of the silver and copper
depositions [8–10]. Nevertheless, they are expected to
be also dependent on copper–silver ratio, on the nature
of the glaze and, when applied over pre-existing
pigments, on the interaction with the underlying
colors.
Here we discuss the results of a study accomplished
on several shards of Italian renaissance lustre pottery
from Deruta and Gubbio. All the samples show the
typical tin-opacified lead glazes decorated with blue
drawings and gold lustre. However, some of them also
show rich and polychrome decorations with blue and
yellow-orange drawings together with gold, red, and
copper-like lustre. These fragments, belonging to
renaissance ceramics from Gubbio (XVI century),
207
show the interesting case of two different attempts
to produce lustre reflection and iridescence, overlapped to a previously pigmented base. The first
example is a common transparent lustre layer overimposed on a blue geometrical drawing, the second is
a (failed) lustre decoration overimposed on a yelloworange flower.
The study widely confirms that lustre is composed
of heterogeneous distributions of copper and silver
nanocrystals and shows that ancient masters were
continuously experimenting for new effects in decorations.
2. Experimental
Analytical investigations were performed using
scanning electron microscopy with energy dispersion
X-ray spectrometry (SEM–EDX), transmission electron
microscopy with energy dispersion X-ray spectrometry
and selected area electron diffraction (TEM–EDX–
SAED), and Vis–UV reflectance spectroscopy.
SEM images, formed using back-scattered electrons (BSE), and EDX analyses have been taken by
a Philips XL30 with an LaB6 source and an EDAX/
DX4 detector.
TEM images, EDX analyses and SAED patterns
have been recorded using a Jeol 2010 operating at
200 kV and having a theoretical point-to-point resolution of 1.9 Å. The EDX spectrometer is equipped with
an ultra-thin window, capable to detect elements
heavier than boron. Electron-transparent sections were
obtained using a Gatan dual ion mill thinner (argon
ions).
Vis–UV reflectance spectra have been recorded
using a JASCO UV/Vis/NIR spectrophotometer model
V-570 equipped with a barium sulfate integrating
sphere.
3. Results and discussion
3.1. The glazes
The analyses of the glazes of all the samples
indicated that they have the typical composition of
the opacified lead glazes, used by Italian masters to
produce lustre pottery in XV and XVI century. Typical
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I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
compositions, as semi-quantitatively determined by
averaging on repeated SEM–EDX analyses performed
on large selected areas are SiO2, 45–65 wt.%; PbO,
15–35 wt.%; Na2O, 1–3 wt.%; K2O, 5–9 wt.%; Al2O3,
2–5 wt.%; CaO, 1–5 wt.%; MgO, 0–0.5 wt.%; FeO,
0.5–2.5 wt.%; SnO2, 5–9 wt.%. As already remarked
in [7], these glazes show a lower lead oxide content
and a relatively larger quantity of alkali, compared to
the typical glazes for Hispano–Islamic lustre pottery
of XIV and XV century.
3.2. The pigments
All the examined samples show brilliant gold lustre
and blue geometrical drawings. Some of them are
polychrome and show lustre and pigments of different
colors. As an example, Fig. 1 shows one of the Gubbio
samples containing gold, red and copper-like lustre,
together with blue drawings and a yellow-orange
decoration consisting of a flower. Although poorly
evident in the picture, lustre reflection and iridescence
are fully attained, when applied over the white-opacified glaze. A brilliant (copper-like) lustre is also
attained, when applied over the blue pigment. Conversely, the yellow-orange flower of Fig. 1 shows
evident lustre metallic reflection only at its borders.
Apparently, the lustre preparation mixture was applied
all over the colored flower. However, lustre was
attained only around the flower on the region of pure
glaze, where no yellow pigment was present.
Fig. 1. Sample of a XVI century pottery from Gubbio, containing
gold, red and copper-like lustre, together with blue geometrical
drawings (a) and a yellow-orange decoration representing a flower
(b). Although not clearly visible in the picture, a brilliant gold
lustre is present all around the flower (b).
As shown in the following, the study of the two
pigments indicated that the blue pigment is smalt,
while that orange-yellow is lead-antimonate (or Giallo
di Napoli). Both pigments were commonly used to
decorate medieval and renaissance ceramics [6,11,12].
3.2.1. The blue smalt
Smalt is an artificial pigment, consisting of a potassium silicate glass with some cobalt oxide. Old recipes
indicate that smalt was prepared first roasting a complex Co–Ni–Fe–As ore, most of the arsenic volatilized
during roasting, then cobalt, nickel and iron oxides
were melted together with siliceous sand [11]. Since
ancient times, smalt was used to color and decorate
glasses, but powdered cobalt glass was also used as
painter pigment. For instance, it was largely used by
Italian painters of XIV and XV century, as shown in
several cases [13,14].
The blue smalt of Deruta renaissance pottery has
already been characterised, in our laboratory, in a
previous work performed on different samples, by
micro-X-ray fluorescence (XRF), XRF with secondary anode, and SEM–EDX [15]. Here the analyses
have been carried out simply by SEM–EDX on crosssections. Fig. 2 shows the typical EDX spectrum of the
blue smalt, with evident peaks of Fe, Co and Ni. Ni
Fig. 2. SEM–EDX spectrum of a blue smalt geometrical drawing.
The presence of copper is due to the lustre overlapped to the blue
geometrical drawing.
I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
and Co are typical elements of the pigment, whereas
Fe can be a constituent of both the glaze and pigment.
Actually, the presence of Fe in the smalt could be
attributed to residues of iron oxide from the mixture
applied to the surface to produce the lustre deposition.
Some of the smalt SEM–EDX spectra, such as that
reported in Fig. 2, show a Cu peak, but this signal was
present only in those regions where lustre was overlapped to the blue pigment. Arsenic was not easily
found. However, careful SEM observations revealed
that crystals of a Ca–Pb–arsenate (Ca:Pb:As close to
30:30:40 at.%) show often association to the blue
smalt in the glaze. The arsenate crystals are up to
10 mm in size and showed a typical hexagonal habit.
The occurrence of arsenate crystals reasonably indicates incomplete As roasting.
The blue smalt was also spectroscopically identified
by visible reflectance measurements. A spectrum is
reported in Fig. 3, where the d ! d band, peaked at
about 600 nm, typical of the electronic spectrum of
smalt, clearly appears. The band is structured in the
three sub-bands originated by Jahn–Teller split transitions 4 A2 !4 T1 ðPÞ in a tetrahedral coordination
[16].
209
3.2.2. The yellow-orange lead-antimonate
Lead-antimonate yellow, also known as Giallo di
Napoli, was frequently used in the manufacturing
of Italian renaissance ceramics, as reported by
Piccolpasso [6]. It is an artificial pigment that has
been manufactured in various periods; dating from
XV century B.C., it was the only yellow colorant and
opacifier in ancient and Mesopotamian glasses.
The most common recipe for its preparation indicates
that a mixture of lead and antimony oxides were
roasted at high temperature [11]. The final color
varied from yellow to orange according to the percentage of the two combined oxides [17]. In this
study, the identification of the pigment was accomplished by SEM–EDX and by TEM–EDX. Fig. 4
reports two BSE–SEM cross-section images, taken at
different magnification. The images well emphasize
the large variety of dimensions of the euhedral
crystals (between 0.5 and 10 mm) containing Pb,
Sb and oxygen, as observed by EDX ðPb : Sb ¼
3 : 2Þ. The chemical composition and the crystalline
nature of the pigment were confirmed by TEM–EDX
and by electron diffraction. A TEM image of small
crystals, with about 500 and 800 nm size, is reported
Fig. 3. Spectrum of a blue smalt drawing as recorded by visible reflectance measurements, using a barium sulfate integrating sphere. Arrows
indicate the typical bands of the pigment (see text).
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I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
Fig. 4. BSE–SEM images of lead-antimonate crystals, taken at
different magnification. The hexagonal crystals are 0.5–10 mm in
size.
in Fig. 5, together with the corresponding EDX
spectrum and SAED pattern.
3.3. The lustre
Lustre was present in all the examined samples. All
the shards showed gold lustre, while some of them, as
the one reported in Fig. 1, also showed red and copperlike metallic reflections.
As previously mentioned, it has been surprisingly
found that lustre consists of a very thin heterogeneous
film of metal nanocrystals dispersed in the glassy
matrix of the glaze [7]. In this work, detailed TEM
images of the lustre layer allowed us to confirm that
lustre has a nanostructural metallic nature, which
shows, in case of gold lustre, well-separated silver
and copper quasi-spherical nanocrystals of variable
diameter, approximately between 5 and 50–100 nm.
Fig. 5. TEM image (a), TEM–EDX spectrum (b) and electron
diffraction pattern (c) of lead-antimonate crystals.
As already reported in [7], silver and copper crystals
are well separated. In general, silver nanocrystals
appear grouped together, to form clusters among a
large number of copper crystals, and are characterised
by larger average dimensions than those of copper.
A typical situation is shown in Fig. 6, where the larger
and darker crystals are observed as silver, while the
others are copper. The typical distribution of silver
I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
211
Fig. 6. TEM image of silver nanocrystals of about 40 nm diameter (black), among smaller (5–10 nm diameter) crystals of copper (grey).
among copper is also shown in Fig. 7, where the SEM
distribution map of the two elements, taken selecting
specific lines of the X-ray emission, is reported.
Although the presence of silver was previously identified by EDX [7], this is a first direct TEM observation
of silver nanocrystals in lustre decorations. It is
worth noting that silver is characterised by nanocrystals that are distributed in regions close to the glaze
surface.
A peculiar property of the lustre is the high density
of the pseudo-spherical metal nanocrystals and their
locally homogeneous distribution. To explain this
point, a typical TEM micrograph of copper nanocrystals is reported in Fig. 8, together with the corresponding SAED pattern. The image shows a homogeneous
distribution of nanocrystals, with an average diameter
10 nm. The nanocrystals are randomly oriented and
some of them show the copper lattice fringes.
The presence of copper and silver nanocrystals can
also be identified by Vis–UV reflection spectroscopy
measurements. In fact, absorption spectra of glass–
metal nanostructured composites are known to show
the typical surface plasmon resonances (SPRs) of
metal nanoclusters dispersed in a glassy medium
[9]. In Fig. 9, a typical Vis–UV absorption spectrum
of a gold lustre layer present in one of our samples is
shown. In the spectrum, both the SPR of silver (around
440 nm) and that of copper (around 560 nm) are
clearly visible. It is known that the peak of the typical
silver SPR is at a wavelength around 400 nm which,
however, can be shifted towards higher wavelength, as
in this case, according to the dimensions of nanocrystals and glaze composition.
3.3.1. Lustre distribution over blue smalt
Well-formed gold and copper-like lustre decorations were frequently found in our samples overlapped
with blue geometrical drawings. As discussed, smalt
pigment consists of a potassium silicate glass with
some cobalt. The glassy nature allows easy dispersion
of the smalt into the glaze, from which appears its
typical color, yet this does not modify other properties.
The quantity of cobalt oxide necessary to get the blue
color is very low; it is well established that 0.01% of
CoO is sufficient to produce a deep blue [11]. Low
concentration blue smalt, well dispersed in the glaze,
does not significantly disturb lustre deposition. Behind
the clearly visible metallic reflection, the presence of a
well-formed lustre overlapped on the pigment is confirmed by the Cu peaks present in the corresponding
SEM–EDX spectra. Moreover, the Vis–UV spectrum
of Fig. 10, which refers to a region where gold lustre
was overlapped on a blue drawing, further confirms
the nanocrystalline nature of the lustre. Both the
typical features of the gold lustre and the blue pigment
are clearly evident. In particular, the SPR of silver at
440 nm is evident, demonstrating the success in nanocrystal formation. On the other hand, the typical SPR
of copper nanocrystals at 560 nm is not visible, but
only because of the significantly overlapped large
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Fig. 8. Copper nanocrystals of about 10 nm diameter in a region of
local homogeneity of the lustre deposition. The first inset shows a
magnification of a 7 nm diameter crystal, with visible copper lattice
fringes. SAED pattern identifies the crystals as metallic copper
(second inset).
Fig. 7. Distribution maps of elemental silver and copper in the
lustre.
band from 550 to 750 nm, typical of the blue pigment
spectrum (see Fig. 3).
3.3.2. Antimonate distribution and lustre
In the case of the orange-yellow flower, lustre effect
was not attained over the flower but only over the white
glaze, immediately close to the pigmented region. In
fact, a careful inspection of the yellow flower maintains
the evidence that lustre deposition was also attempted
on the flower but without any success.
First of all, at a simple visual inspection, a brilliant
gold lustre is present at the border of the yellow flower,
but it does not abruptly finish when the yellow flower
begins, showing a gentle decrease up to its disappearance. Second, accurate BSE–SEM observations indicate that few silver crystals are sometimes present in
the yellow flower region, but only in the rare and small
areas which appear fully free from lead-antimonate
crystals. To support this view, in Fig. 11 it is reported a
BSE–SEM image of a cross-section of a region where
silver clusters are present over the yellow flower, far
from its border. The image makes evident the presence
of the lead-antimonate crystals and the presence of
small silver crystals, identified by EDX, close to the
glaze surface, but only in the small region free from
the lead-antimonate.
As already shown in Fig. 4, lead-antimonate crystals are large (up to 10 mm) and deeply penetrated into
the glaze. Their intrusion apparently produces significant alterations of the glaze surface, hindering the
formation of the lustre.
I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
213
Fig. 9. Absorption spectrum of a gold lustre decoration as recorded by visible reflectance measurements. The SPRs of silver and copper
nanocrystals dispersed in the glassy matrix of the glaze are indicated.
Fig. 10. Absorption spectrum of a gold lustre overlapped to a blue geometrical drawing as recorded by visible reflectance measurements. The
SPR of dispersed silver and copper nanocrystals are indicated. The copper SPRs appears overlapped to the large absorption band of the blue
smalt pigment.
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I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
Fig. 11. BSE–SEM image of the region of the yellow flower far from the border characterised by the presence of brilliant gold lustre. The
image puts clearly in evidence the presence of the lead-antimonate crystals (a) and the presence of small silver crystals (b) identified by EDX,
close to the glaze surface where lead-antimonate is lacking.
The yellow pigment crystals produce further modifications of the glaze properties. Tin dioxide, as
cassiterite, is normally present in the glaze as opacifier. However, SEM–EDX analyses in the region of the
antimonate pigment did not show any presence of tin,
being tin present in the surrounding parts. Therefore,
we conclude that application of the pigment moved tin
dioxide towards the adjacent regions or, alternatively,
that the presence of antimonate passivated the tin
dioxide recrystallization. To understand this point,
we remind that, when glaze is fired, tin dioxide first
melts within the lead silicate, in the temperature range
600–650 8C; then, in the range 700–750 8C, starts to
recrystallize and remains crystalline during heating up
to and cooling down from 1200 8C [18].
3.3.3. Comment on lustre formation
As mentioned in Section 1, a strong analogy exists
between composition and microtexture of lustre and
that of silicate glasses containing metal clusters, which
have attracted interest in recent years as materials for
non-linear optical device fabrication [8]. Therefore,
although the nanocluster formation mechanism in a
glassy matrix is still under debate, some simple considerations on lustre formation can be drawn on the
basis of the recent studies on metal nanocrystals,
produced in ion-bombarded pure silica [19], in sol–
gel depositions on silica [20], or in silver–sodium
exchanged glasses [21], thermally treated in a reducing atmosphere. Most of these studies have been
recently carried out to study the physics and the
chemistry of nanocrystal formation, the crystal structure and properties, the crystal–matrix interaction and
the general metal–glass composite properties for
optoelectronics applications. It has been found that
the structure, size and size distribution of nanocrystals
mainly depend on the nature of the ions and their
interaction with the matrix and the environment, while
the aggregation behavior is determined by the temperature and by the electronic, thermal and structural
properties of the glass and the ions [22].
In spite of the complex nature of nanocrystal formation mechanism, following the indications of these
works, it appears quite reasonable that the first step of
lustre formation consists of an ion-exchange between
the alkali ions present in the glaze [7] and silver and
copper ions present in the mixture of the lustre recipe
[6]. The second step could then be the reduction of the
ions, as produced by thermal annealing and/or by
reducing atmosphere.
Actually, silver–sodium and copper–sodium ionexchange has been documented to occur efficiently
at the surfaces of glasses immersed in a molten salt
mixture, even for low salt concentration [21] and the
ion-exchange technique has been successfully applied
to develop special glasses with high specific proper-
I. Borgia et al. / Applied Surface Science 185 (2002) 206–216
215
ties, by replacing alkali ions with other monovalent
cations [22]. First crystal nucleation is, therefore,
expected to be originated by a spontaneous reaction
of the ions in the matrix, as produced by an external
reducing agent, possibly created in the kiln by the
introduction of smoking organic substances, at about
600 8C [6,7]. In fact, recent experimental evidences
has shown that Agþ and Cuþ ion-implanted or ionexchanged glasses, at around 600 8C in a reducing
atmosphere (5% H2 in N2), easily produce metal
nanoclusters [11,23,25]. After the first nucleation,
the growth can be regarded as a process due to the
supersaturation of the crystal constituent concentrations in the region where clustering occurs [24,26].
Although certainly oversimplified, this description
rationalizes the results obtained in this work and in the
recent study on lustre surfaces in Spanish and Italian
pottery from XIV to XVI century [7]. In particular, this
description allows us to explain the lacking lustre in
the yellow pigment region as due to the large yellow
pigment crystals which obstacle the primary alkalisilver/copper ion exchange, thus avoiding a significant
nucleation and growth of metal nanocrystals. Conversely, the process is not hindered by the glassy blue
smalt, due to its diffusion into the glaze and low
concentration.
observed that lustre nanocrystals are deposited, overlapped to a possible underlying pigment, when the
pigment is finely dispersed in the glaze at low concentration. This occurs in the case of the cobalt
blue drawings on the glaze. However, when yellow
coloured decorations are obtained by large lead-antimonatecrystals, the formation of lustre nanocrystals
is strongly hindered. Thus, a gold lustre is attained
only at the border of the yellow decoration, where the
large antimonate crystals are not present. Few silver
crystals have been observed, by a careful SEM and
TEM inspection, among the yellow pigment crystals
at the surface of the glaze. However, their very low
density does not allow to obtain any metallic lustre
effect.
In terms of a simple model, suggested by the
analogy of lustre and modern synthesized nanostructured metal–glass composites, the large antimonate
crystals hinder lustre formation, possibly avoiding the
initial penetration of silver and copper ions into the
glaze. It is found that yellow lead-antimonate even
hinders the crystallization of tin dioxide which, however, is normally present in the glaze as opacifier in the
volume surrounding the pigmented region.
4. Conclusion
The authors wish to thank C. Centroni, G. Benazzi
and S. Quercia of the Soprintendenza ai
BB.AA.AA.AA.SS. dell’Umbria, M. Mastice, Major
of Deruta, G. Busti of the Museo Regionale della
Ceramica di Deruta, and Suor Clotilde of the Monastero di S.Anna in Foligno for providing us the
samples of the present study. Many thanks to
P. Mazzoldi, R. Bertoncello, G. Battaglin, F. d’Acapito,
G. Biscontin and B. Fabbri for fruitful discussions on
lustre as a metal–glass composite. Special thanks to
M. Vendrell, J. Molera and J. Perez for very helpful
discussions on lustre pottery, on tin-opacified lead
glazes, and for illuminating comparisons with the
Hispano–Islamic lustre technique.
In conclusion, an extended study has been carried
out on several samples of medieval and renaissance
lustre pottery from Deruta and Gubbio.
The glaze shows the typical composition used by
Italian masters for lustre depositions, with the presence of a relatively larger quantity of alkali compared
to the glazes of Hispano–Islamic lustre pottery.
Lustre is confirmed to be characterised by a heterogeneous distribution of silver and copper nanocrystals,
which, however, show regions of local homogeneity.
TEM images show that silver nanocrystals are well
separated from those of copper and have a quasispherical shape, with an average diameter larger than
that of copper nanocrystals. Vis–UV spectra showed
the typical SPR of the nanostructured silver–copper
glass–metal composites.
Some shards have drawings of blue smalt and yellow
decorations made by a lead-antimonate pigment. It is
Acknowledgements
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